Multilayer LC filter with improved magnetic coupling characteristics

ABSTRACT

A multilayer LC filter includes two LC resonance circuits ( 21  and  22 ) in a two-stage circuit configuration. First and second resonator inductors (L 21  and L 22 ) formed by two strip-like electrical paths ( 14  and  15 ) extend laterally in parallel and are patterned on the same inductor layer (c). A strip-shaped shielding or ground path ( 35 ) is formed between, and in parallel with, the two strip-shaped electrical paths ( 14  and  15 ) such that the electrical paths are in the shape of a fork on the inductor layer c. The magnetic coupling between the resonator inductors (L 21  and L 22 ) is thus weakened and, even when pattern dislocations occur during the patterning of the paths, there is substantially no variation in the magnetic coupling characteristics of multilayer LC filters of this construction.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a multilayer LC filter for use in mobile communication devices such as cellular phones.

[0003] 2. Description of the Related Arts

[0004] Various small-sized LC filters for use in mobile communication devices such as cellular phones have hitherto been proposed which feature low losses and are capable of high mass-productivity. A circuit diagram for such a LC filter is shown in FIG. 5, where a multilayer LC filter A′ comprises an input/output line M connecting an input terminal 3 and an output terminal 4, with three capacitors C being connected in series in the input/output line M, and with another capacitor C being connected in the input/output line M in parallel with the above-mentioned capacitors. Two LC resonance circuits 1 and 2, in a two-stage circuit configuration, are connected across the three capacitors C with both of the circuits 1 and 2 being grounded. The LC resonance circuit 1 on the side of the input terminal 3 comprises a resonator capacitor C1 and a resonator inductor L1, and the LC resonator circuit 2 on the side of the output terminal 4 comprises a resonator capacitor C2 and a resonator inductor L2. In this configuration, the resonator capacitor C1 and the resonator inductor L1 are connected in parallel with each other, and the resonator capacitor C2 and the resonator inductor L2 are connected in parallel with each other, with the resonator inductors L1 and L2 of the LC resonance circuits 1 and 2 being coupled magnetically to each other.

[0005] Referring to FIG. 6, which is an exploded perspective view of the physical construction of the multilayer LC filter A′, filter A′ is a laminate which includes a plurality of conductive electrical paths 9, and electrodes 10, with dielectric layers disposed therebetween. More particularly, the multilayer LC filter A′ is preferably obtained by patterning and laminating predetermined conductive electrical paths 9 and electrodes 10 on dielectric sheets and by integrating all of them into a single-piece construction. Specifically, in this process, two strip-like electrical paths 5 and 6, constituting the resonator inductors L1 and L2 of FIG. 5, are patterned as strips extending in laterally spaced parallel relation to each other on the same dielectric layer. The ends of the strip-like or strip-shaped electrical paths 5 and 6 are respectively connected to electrical paths 9 a and 9 b, constituting the resonator capacitors C1 and C2 of FIG. 5, patterned on another dielectric layer. The other base ends of paths 5 and 6 are connected to a ground electrode 10 a at the lowest position in the laminated structure that forms filter A′ through a strip-shaped lead or electrical path 7 which extends from an integrally-formed path portion 8 which extends orthogonally to, and is electrically connected to, these base ends.

[0006] The electrical paths for the resonator inductors, and other conductive components, in the above-discussed LC resonance circuit are generally patterned on the corresponding dielectric sheets by using a conventional screen printing technique or process. However, in using the screen printing process for patterning the electrical paths for the resonator inductors and other components, the effective lengths of the electrical paths for the resonator inductors may vary because of the process. Specifically, this variation can be caused by dispersion of the material used in the process. Further, the short-circuiting positions of the electrical paths may vary because of dislocations occurring in associated processes such as cutting. These problems are sometimes referred to as “pattern dislocation.” Such pattern dislocations cause a variation in the magnetic coupling characteristics between the resonator inductors disposed on the LC resonance circuit.

[0007] Referring to FIG. 7, examples of the effects of such pattern dislocation are presented. In FIG. 7, in a situation wherein the strip-like electrical path for the resonator inductor is dislocated by 30 μm in the direction in which the strip-like electrical path extends toward the side where the resonator capacitors C1 and C2 are connected (hereinafter referred to as “+ direction”), the value of 2.5 dbBW (MHz) varies from 76.0 MHz to 98.0 MHz (a variation range of 22.0 MHz), the value of TOP L (db) varies from 2.27 db to 2.23 db (a variation range of −0.04 db) and the value of R. L. (db) varies from 15.4 db to 12.7 db (a variation range of −2.7 db). To briefly explain these values, 2.5 dbBW (MHz) is a value representing the bandwidth of the filter when the attenuation drops from 0 db to 2.5 db, while TOP L (db) is a value representing the minimum insertion loss in the pass band of the filter and R. L. is a value representing the value of the reflective attenuation in the pass band of the filter.

[0008] Such variation in the magnetic coupling characteristics of the multilayer LC filters during manufacture results in a variation in the quality of the multilayer LC filters and this leads to an increase in manufacturing costs where additional processing is needed for correction of the magnetic coupling characteristics.

SUMMARY OF THE INVENTION

[0009] The present invention is concerned with the problems discussed above and it is, therefore, an object of the present invention to provide a multilayer LC filter in which pattern dislocations which occur during patterning of the conductive elements or components thereof only minimally contribute to variations in the magnetic coupling characteristics of the associated LC resonance circuit or circuits.

[0010] According to a first aspect of the present invention, there is provided a multilayer LC filter comprising a first LC resonance circuit having a first resonator inductor; and a second LC resonance circuit having a second resonator inductor; the first resonator inductor and the second resonator inductor being comprised of two strip-shaped electrical paths, i.e., elongate electrically conductive elements, extending in laterally spaced parallel relation and patterned on the same dielectric layer, with the base end of each strip-shaped electrical path being connected to the ground, wherein a strip-shaped shielding ground electrical path is formed between, and disposed in parallel with, the first resonator inductor and the second resonator inductor.

[0011] The first resonator inductor and the second resonator inductor, comprised of the two strip-shaped electrical paths patterned in laterally spaced, parallel relation on the same dielectric layer, are magnetically coupled together. As indicated above, in this configuration, a shielding ground electrical path according to the invention is connected to ground and formed between, and disposed in parallel with, the resonator inductors. As a consequence, the amount of variation in magnetic coupling caused by pattern dislocation can be made smaller than that in a conventional structure which does not include the shielding ground electrical path.

[0012] For example, as shown in FIG. 3, when the strip-shaped electrical path of the resonator inductor is dislocated by 30 μm in the + direction, the value of 2.5 dbBW (MHz) varies only by 5.0 MHz, the value of TOP L (db) varies only by −0.02 db and the value of R. L. (db) varies only by −1.0 db.

[0013] Comparing the aforementioned variation ranges for these magnetic field characteristics with that of a conventional configuration, as set forth in FIG. 7, it can be seen that the multilayer LC filter of the invention has a smaller variation range for each characteristic and has a reduced variation in the characteristics of the magnetic coupling relative to the pattern dislocations. For example, when the strip-shaped electrical path of the resonator inductor is dislocated by 30 μm in the + direction, the variation range of the 2.5 dbBW characteristic of the invention is reduced by 17.0 MHz as compared with that of the conventional configuration.

[0014] By virtue of a configuration wherein an integrally-formed portion and a strip-shaped lead electrical path are also patterned on the same dielectric layer, and the integrally-formed portion is connected to and extends transversely with respect to the base ends of the shielding earth electrical path, the first resonator inductor and the second resonator inductor (all of which extend in parallel with each other), and the strip-shaped lead electrical path extends outwardly from the integrally-formed portion toward the opposite side of the dielectric layer away from the side where the resonator inductors are formed, the resonator inductors of the LC resonance circuits and the electrical paths for grounding the resonator inductors can all be formed on a single dielectric layer. It is thus possible to reduce the number of the layers or laminations of the multilayer LC filter and to thus meet the ever present need for a lower filter profile and a smaller filter size.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Other objects, aspects, features and advantages of the present invention will be described in or apparent from the following detailed description of preferred embodiments thereof, when taken in conjunction with the accompanying drawings, in which:

[0016]FIG. 1 is an equivalent circuit diagram of a multilayer LC filter according to a preferred embodiment of the invention;

[0017]FIG. 2 is an exploded perspective view showing a multilayer LC filter according to a preferred embodiment of the invention;

[0018]FIG. 3 is a chart showing the magnetic characteristics of the multilayer LC filter according to a preferred embodiment of the invention;

[0019]FIG. 4 is a cross-sectional view showing a particular inductor layer of the multilayer LC filter of FIG. 2;

[0020]FIG. 5, which was described above, is an equivalent circuit diagram of a conventionally structured multilayer LC filter;

[0021]FIG. 6, which was also described above, is an exploded perspective view of the conventionally structured multilayer LC filter; and

[0022]FIG. 7, which was also described above, is a chart showing the magnetic characteristics of the conventionally structured multilayer LC filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] One embodiment of the multilayer LC filter according to the present invention will now be described with reference to the accompanying drawings. As shown in FIG. 1, a multilayer LC filter A, according to the invention, comprises an input/output line M connecting an input terminal 11 and an output terminal 12. The input/output line M is supplied with a high frequency voltage and connected thereto are two input/output coupling capacitors C11 and a “between-the-stages” coupling capacitor C14 connected between the two input/output coupling capacitors C11. Capacitors C11 and C14 are all connected in series as shown.

[0024] In addition, two LC resonance circuits 21 and 22, of a two-stage configuration, are connected, respectively, across each of the input/output coupling capacitors C11 and the between-the-stages coupling capacitor C14. The first LC resonance circuit 21 is connected on the side of the input terminal 11, the second LC resonance circuit 22 is connected on the side of the output terminal 12, and each of the LC resonance circuits 21 and 22 are grounded.

[0025] The first resonance circuit 21 is formed by a first resonator capacitor C21 and a first resonator inductor L21, with the first resonator capacitor C21 and the first resonator inductor L21 being connected in parallel with each other. The second resonance circuit 22 is formed by a second resonator capacitor C22 and a second resonator inductor L22, with the second resonator capacitor C22 and the second resonator inductor L22 being connected in parallel with each other.

[0026] As will be described in more detail below, the first and the second resonator inductors L21 and L22 of the resonance circuits 21 and 22 are disposed in coupling relation to each other on the same dielectric layer of the filter such that there is magnetic coupling therebetween. Further, a polarity-generating capacitor C13 is connected across the input terminal 11 and the output terminal 12 and in parallel with the capacitors C11 and C14.

[0027] The multilayer LC filter A according to the invention is of a multilayer construction shown in FIG. 2. More specifically, the filter A is constructed such that electrical paths or conductive elements 13 to 24, 35 and 36 and electrodes or conductive elements 25 to 32, constituting the above-described capacitors C11, C13, C14, C21 and C22, resonator inductors L21, L22, and so on, are disposed one upon another with dielectric layers interposed therebetween.

[0028] At the bottom or lowest position of the multilayer LC filter A as viewed in FIG. 2, a terminal layer a is provided which comprises an input terminal electrode 25 acting as the input terminal 11, an output terminal electrode 26 acting as the output terminal 12, ground terminal electrodes 27 and 28 adapted to be grounded, i.e., connected to ground, and terminal electrodes 29, 30, 31 and 32 connected to predetermined electrical paths. As illustrated, electrodes 25, 26, 27, 28, 29, 30, 31 and 32 are exposed at the bottom surface of the multilayer LC filter A, with a side or lateral electrode (not shown) formed integrally with these electrodes extending along the side surface of the multilayered body forming filter A.

[0029] Above the terminal layer a are formed, in the order mentioned, a ground electrode layer b, an inductor layer c, capacitor layers d, e and f, a ground electrode layer g, a capacitor layer h, and a ground electrode layer i, with a dielectric layer j providing the upper or top surface of the multilayer LC filter A at the top or uppermost or topmost position thereof. The electrical paths 13, 21 and 24 of the ground electrode layers b, g and i act as ground electrodes and are formed by conductive patterning thereof on the respective layers in order to enhance the shielding capability of the multilayer LC filter A.

[0030] The electrical paths 21 and 22 and the electrical paths 21 and 23, respectively, of the capacitor layer h and of the ground electrode layer g constitute the first and the second resonator capacitors C21 and C22 of the first and the second LC resonance circuits. The first and the second resonator capacitors C21 and C22 constituted by the electrical paths 21, 22 and 23 are consequently grounded.

[0031] Electrical paths 17 and 19 and electrical paths 18 and 20 of the capacitor layers e and f constitute respectively the input/output coupling capacitors C11 and C11. Further, the between-the-stages coupling capacitor C14 is of a distributed configuration disposed between the electrical path 17 and the electrical path 18. The electrical paths 16, 17 and 18 of the capacitor layers d and e constitute the polarity-generating capacitor C13.

[0032] The principal aspects of the present invention will next be described.

[0033] The first resonator inductor L21 is constituted by a strip-like or strip-shaped electrical path 14 of the inductor layer c and the second resonator inductor L22 is constituted by a strip-like or strip-shaped electrical path 15. The first resonator inductor L21 and the second resonator inductor L22 are patterned on the same dielectric layer (inductor layer c) such that they extend in laterally spaced relation, in parallel with each other to produce a magnetic coupling therebetween. The distal ends of the electrical paths 14 and 15 (shown at the far side of FIG. 2) are connected respectively to the electrical paths 22 and 23 of the capacitor layer h and the electrical paths 19 and 20 of the capacitor layer f.

[0034] A strip-shaped shielding ground electrical path 35 is formed between, and in parallel with, the strip-shaped electrical paths 14 and 15 of the resonator inductors L21 and L22. The distal end of this shielding ground electrical path 35 (shown at the far side of FIG. 1) is connected to the ground terminal electrode 28 of the terminal layer a.

[0035] Further, the other ends (shown at the closer side of FIG. 2) of the shielding ground electrical path 35, the first resonator inductor L21 (strip-shaped electrical path 14) and the second resonator inductor L22 (strip-shaped electrical path 15) all extend in parallel with each other and are connected together electrically by an integrally-formed portion or conductive path 37 which extends to and transversely connects the base ends of the paths 35, 14 and 14 together. A strip-shaped lead electrical path 36 is patterned to extend from the integrally-formed portion 37 toward the opposite side of, i.e., away from, the electrical paths 14 and 15. This lead electrical path 36 is connected to the ground terminal electrode of the terminal layer a. Therefore, the resonator inductors L21 and L22 (the strip-shaped electrical paths 14 and 15) are connected to the capacitors C11, C21 and C22 on one side and are grounded on the other side.

[0036] In the manner just described, as shown more clearly in FIG. 4, a fork-shaped electrical path or pattern is provided on the inductor layer c formed with the resonator inductors L21 and L22 of the LC resonance circuits 21 and 22.

[0037] The multilayer LC filter A is obtained by patterning predetermined electrical paths on dielectric sheets using screen printing techniques and the like, by laminating the plurality of dielectric sheets together and by integrating (by, e.g., calcination), all of the sheets into a single-piece construction. The dielectric sheets are preferably in the form of kneaded sheets consisting of dielectric powder and magnetic powder together with a binding agent and the like. The electrical paths are preferably made of electrically conductive materials in a paste form such as Ag, Pd, Cu, Ni, Au, and Ag—Pd pastes.

[0038] A comparison will now be made between the magnetic characteristics of the multilayer LC filter A according to the invention and the magnetic characteristics of the conventionally constructed multilayer LC filter A′ described above.

[0039] As shown in the aforementioned FIG. 7, with the conventionally constructed or structured multilayer LC filter A′, when the strip-shaped electrical paths 5 and 6 of the resonator inductor L1 and L2 are dislocated by 30 μm in the direction in which the strip-shaped electrical paths 5 and 6 are formed, i.e., toward the side where paths 5 and 6 are connected to the resonator capacitors C1 and C2 (referred to, as indicated above, the + direction), the value of 2.5 dbBW (MHz) varies as much as 22.0 MHz, the value of TOP L (db) varies by −0.04 db and the value of R. L. (db) varies by −2.7 db. When the electrical paths 5 and 6 are dislocated by 30 μm toward the lead electrical path 7 (hereinafter referred to as the − direction), the value of 2.5 dbBW (MHz) varies as much by −27.0 MHz, the value of TOP L (db) varies by 0.10 db and the value of R. L. (db) varies by 4.1 db.

[0040] On the other hand, as shown in FIG. 3, with the multilayer LC filter A according to the invention, when the electrical paths 14 and 15 of the resonator inductor L21 and L22 are dislocated by 30 μm in the direction in which the electrical paths 14 and 15 are formed, i.e., toward the side where paths 14 and 15 are connected to the resonator capacitors C21 and C22 (the + direction), the value of 2.5 dbBW (MHz) varies only by 5.0 MHz, the value of TOP L (db) varies by −0.02 db and the value of R. L. (db) varies by −1.0 db. In addition, when the electrical paths 14 and 15 are dislocated by 30 μm toward the lead electrical path 36 (the − direction), the value of 2.5 dbBW (MHz) varies only by −6.0 MHz, the value of TOP L (db) varies by 0.02 db and the value of R. L. (db) varies by 1.3 db.

[0041] It will be seen from the foregoing that when the variation ranges of the characteristics are compared to those of the conventionally structured multilayer LC filter A′, the variation ranges of the multilayer LC filter of the invention are smaller and the variation of the magnetic coupling characteristics versus pattern dislocations is reduced. More specifically, when the electrical paths 14 and 15 of the resonator inductor L21 and L22 are dislocated by 30 μm in the + direction, the variation ranges of the multilayer LC filter according to the invention are reduced, as compared to those of the conventionally structured multilayer LC filter, by 17.0 MHz for the value of 2.5 dbBW (MHz), by 0.02 db for the value of TOP L (db) and by 1.7 db for the value of R. L. (db). On the other hand, when the electrical paths 14 and 15 are dislocated by 30 μm in the

[0042] direction, the variation ranges of the multilayer LC filter according to the invention are reduced, as compared to that of the conventionally structured multilayer LC filter, by 21.0 MHz for the value of 2.5 dbBW (MHz), by 0.08 db for the value of TOP L (db) and by 2.8 db for the value of R. L. (db).

[0043] Thus, because of the configuration including the shielding ground electrical path 35, a multilayer LC filter can be provided which does not suffer from substantial variation in the magnetic characteristics thereof even when pattern dislocations have occurred during the screen printing process used for patterning the electrical paths 14 and 15 constituting the resonator inductors L21 and L22 of the LC resonance circuits 21 and 22.

[0044] Further, the multilayer LC filter A according to the invention also allows adjustment of the magnetic characteristics of the multilayer LC filter A. In other words, a method for adjusting the magnetic characteristics of the multilayer LC filter A is provided in which desired values can be set for the magnetic characteristics of the multilayer LC filter by varying the strip length or the strip width of the lead electrical path 36 or the shielding ground electrical path 35. For example, the magnetic coupling provided is made weaker as the strip length or strip width of the lead electrical path 36 is increased. Therefore, an adjustment can be made for weakening the effect of variations in magnetic coupling characteristics caused by pattern dislocations. On the other hand, in order to enhance the magnetic coupling, the strip length of the lead electrical path 36 may be made as short as possible, for example. In one important embodiment, the strip-shaped shielding ground path 35 is of a greater width than paths 14 and 15, as shown in FIG. 4.

[0045] The techniques used for patterning the electrical paths or electrodes on the dielectric sheets can be known, conventional methods such as sputtering and vacuum deposition, in addition to conventional screen printing techniques.

[0046] It will be appreciated that the multilayer LC filter according to the invention is not limited to the above-described embodiment but can be variously modified within the scope of the invention and without departing from the spirit of the invention.

[0047] Because the multilayer LC filter according to the invention is constructed such that the strip-shaped shielding ground electrical path is formed between, and in parallel with, the first resonator inductor and the second resonator inductor, the amount or rate of the variation in the magnetic coupling caused by the pattern dislocations is reduced as compared to that of a conventionally structured multilayer LC filter which does not include such a shielding ground electrical path.

[0048] In the case where the multilayer LC filter according to the invention comprises the integrally-formed portion extending transversely to and electrically connecting together the base ends of the shielding ground electrical path, and the electrical paths form the first resonator inductor and the second resonator inductor, extending in parallel with each other, and strip-shaped lead electrical paths extend from the integrally-formed portion toward the opposite side of the side from that at which the resonator inductors are formed, it is possible to form, on a single dielectric layer or sheet, the resonator inductors of the LC resonance circuits and lead electrical paths for grounding the resonator inductors. It is thus possible to reduce the number of the layers of laminations in a multilayer LC filter and to thus meet the ever present need for an LC filter of a lower profile and a smaller size. 

What is claimed is:
 1. A multilayer LC filter comprising: a first LC resonance circuit having a first resonator inductor; and a second LC resonance circuit having a second resonator inductor; the first resonator inductor and the second resonator inductor comprising first and second strip-shaped electrical paths extending in laterally spaced, parallel relation and patterned on a common dielectric layer, each electrical path having a base end connected to ground, and said filter further comprising a strip-shaped shielding ground electrical path formed between, and disposed in parallel with, the first and second resonator inductors.
 2. The multilayer LC filter according to claim 1, wherein an integrally-formed connecting portion and a strip-shaped lead electrical path are patterned on said common dielectric layer, the integrally-formed portion extending transversely to and being electrically connected to the base ends of the shielding earth electrical path, the first resonator inductor and the second resonator inductor, and the strip-shaped lead electrical path extending outwardly from the integrally-formed portion toward a side of the common layer at which the resonator inductors are formed.
 3. The multilayer LC filter according to claim 1, wherein the strip-shaped shielding ground electrical path has a larger width than that of the first resonator inductor and the second resonator inductor.
 4. A multilayer LC filter comprising: a first LC resonance circuit including a first resonator inductor; and a second LC resonance circuit including a second resonator inductor; the first resonator inductor and the second resonator inductor comprising first and second elongate electrically conductive elements disposed in laterally spaced, parallel relation on a common dielectric layer, each electrical element having a base end connected to ground, and said filter further comprising a further elongate electrically conductive element formed on said common dielectric layer between, and in parallel, equally spaced relation with, the first and second elements, said further element being connected to ground.
 5. The multilayer LC filter according to claim 4 wherein said further element includes a base end, and said filter further comprises a connecting portion formed integrally with said elements on said common dielectric layer, said connecting portion extending transversely to, and being electrically connected to, the base ends of the further element and the first and second elements.
 6. The multilayer LC filter according to claim 5 further comprising a further portion formed integrally with said connecting portion on said common dielectric layer and extending outwardly from said connecting portion in a direction away from said elements.
 7. The multilayer LC filter according to claim 4 wherein said further element is of greater width than said first and second elements. 